The invention is directed to a method and composition for the preparation of molded polyurethane and/or polyurea articles. More particularly, this invention concerns a method and composition for the preparation of molded polyurethane and/or polyurea articles, which may optionally have a cellular core, by the reaction of at least one polyol or one polyamine with an organic di- or polyisocyanate in the presence of a catalyst, release agent and optionally conventional additives such as cross linking agents, chain extenders, blowing agents, stabilizers, cell regulators, pigments and fillers.
Molded polyurethane articles or molded polyurethane foams are obtained by the reaction of at least one polyol (polyether or polyester polyol) with an organic di- or polyisocyanate. The corresponding molded polyurea articles are obtained by the reaction of a polyamine, such as a polyoxypropylenediamine, with an organic di- or polyisocyanate. Molded articles which contain urethane as well as urea groups, can be produced in a known manner according to the state of the art by reacting polyols with organic di- or polyisocyanates in the presence of amine cross linking agents.
Articles of molded polyurethane or polyurea are used on a large scale as car body parts such as skirt, spoiler, fenders or for the manufacture of seats for the automobile industry. Because of their toughness and wear resistance, polyurethane and polyurea polymers can also be used for the manufacture of shoe soles, heels and similar products.
Curing of polyurethane and polyurea products frequently takes place simultaneously with molding in closed heated molds. Such procedures, particularly the reaction injection molding method, which is also referred to as the RIM method, have gained special importance.
An appreciable problem occurs from the fact that molded polyurethane articles tend to adhere to the inner wall of the mold. A large number of release agents are known to those skilled in the art of manufacturing molded articles from reactive compositions which may be applied on the inner walls of the molds or added as internal release agents to the reaction formulation. Internal release agent, which generally belong to different classes of substances from those applied to molds, include for example, metal soaps, such as zinc stearate, esters of higher fatty acids, natural or synthetic oils, waxes and silicones.
Especially preferred internal release agents are those which make any special preparation of the molds superfluous, do not affect the properties of the reacted, molded synthetic material and, as far as possible, cause no change of the surface properties of the molded articles, such as an adverse effect on paintability. The internal release agents must be readily dispersible in the reaction formulation; but to be effective, they must also accumulate at the surface of the molded article.
Examples of internal release agents which are used particularly for the production of molded polyurethane or polyurea articles by the RIM method are organosilicon block copolymers which, aside from siloxane blocks, have polyoxyalkylene blocks. In this connection, the structure of the compounds evidently plays an essential role in the release behavior.
For example, it may be inferred from the German Offenlegungsschrift 2,543,638 that compounds of the formula ##STR1## are inferior to compounds of the formula ##STR2## In formulas III and IV, subscript x in each case has an average value of 3 to 45, subscript y an average value of 8 to 198, Me represents methyl and the (--OR).sub.x group represents a polyoxyalkylene polymer or a polyoxyalkylene copolymer, wherein R is composed of ethylene groups or butylene groups or mixtures of ethylene or butylene groups with propylene groups, the ratio of the amount of ethylene or butylene groups to the amount of propylene groups being selected so that the ratio of the carbon atoms to the oxygen atoms in the whole of the (--OR--) block is 2.0:1 to 2.9:1.
Test methods for determining and comparing the release properties of different release agents can also be taken from this Offenlegungsschrift.
The internal release agents on the market are not satisfactory in all respects and it would be desirable if the release properties were to be improved further.
An additional disadvantage of known internal release agents is that, in the manufacture of the molded polyurethane articles with a cellular core, they hinder the development or retention of the cellular structure and, in the limiting case, cause foam that is formed to collapse. However, the development of a cellular structure in the interior of the molded article is important in order to obtain molded articles which have a satisfactory surface, as well as satisfactory mechanical properties.
Some manufacturers desire release agents which are free of SiOSi bonds, since there is concern about possible interference with the later processing of the molded article, for example, when painting. It is therefore desirable to make highly effective silicon-free release agents available to manufacturers.